This invention relates generally to parallel-acting roller clamps for regulating fluid flow through a deformable plastic tube in an intravenous (I.V.) administration set, and, more particularly, to parallel-acting roller clamps configured to provide improved control of fluid flow rate.
Parallel-acting roller clamps of this kind are commonly used as part of I.V. administration sets, for regulating the flow of a fluid being infused through a plastic infusion tube into a patient. The tube typically is formed of polyvinyl chloride (PVC) and is readily deformable. Such clamps typically include an elongated body having left and right side walls and a bottom wall, which cooperate to define an elongated chamber. A knurled roller wheel is located within the elongated chamber, with the ends of a wheel axle being supported within trunnion grooves formed in the left and right side walls. These grooves are arranged generally parallel with the bottom wall. The roller wheel, thereby, can be manually rolled along an axis substantially parallel with the bottom wall, while pinching the plastic infusion tube between the roller wheel and a clamping surface of the bottom wall. A relief groove is formed along the length of the bottom wall, having a transverse width that tapers from a maximum value at a first end to a minimum value at a second, opposite end. The relief groove typically is located along the centerline of the bottom wall, and the bottom wall's clamping surface is located on the left and right sides of such relief groove.
The body and roller wheel of the roller clamp are sized and configured such that the portions of the infusion tube sandwiched between the wheel and the clamping surface are pinched fully shut, while the portion of the infusion tube overlaying the relief groove is accommodated by the relief groove, to form a lumen for the flow of fluid. The size of the lumen, and thus the rate of fluid flow, is determined by the width of the relief groove immediately beneath the roller wheel.
Typically, the relief groove has a triangular cross-section defined by a pair of inclined walls, and the width of this relief groove tapers uniformly from its first end to its second end. Thus, the flow rate of fluid through the infusion tube can be made to vary from a maximum value, when the roller wheel is located at the relief groove's first end, to a minimum value, when the roller wheel is located at the relief groove's opposite, second end.
Parallel-acting roller clamps of this kind have functioned generally satisfactorily in regulating the flow of fluids being infused into patients. However, cold flow, or creep, of the portion of the plastic infusion tube being pinched by the roller wheel can, under certain circumstances, unduly affect the size of the formed lumen, and thus the stability of the fluid flow rate. Total flow rate variations in the range of 10 to 20 percent are generally considered acceptable; however, in some cases, unacceptably higher flow rate variations have been observed. Typically, about half of the total flow rate variation due to cold flow occurs within about 10 minutes after a flow rate adjustment has been made, with the remainder occurring over the next hour.
It should be appreciated from the foregoing description that there is a need for an improved parallel-acting roller clamp of a kind that minimizes variations in flow rate over time, due to cold flow or creep of its deformable plastic tube. The present invention satisfies this need and provides further related advantages.